Gene therapy approaches rely on the efficient transfer of genes to the desired target cells. In order to increase efficiency, researchers have explored ways to use both viral and non-viral vectors.
One of the areas that researchers have explored with great interest is the use of lentiviral vectors. Lentiviral vectors make use of lentiviral polynucleotide sequences and are a subclass of retroviral vectors. However, unlike other retroviruses, lentiviruses are able to integrate into the genome of non-dividing cells. After entry into a cell, the viral genome, which is in the form of single-stranded RNA, is reverse transcribed to generate a double-stranded DNA, which is then inserted into the host genome. Because lentiviral vectors can cause their sequences to be integrated into non-dividing cells, they provide particularly promising leads for gene therapy.
Another area of interest for researchers is RNA inference, also referred to as RNAi, which involves the phenomenon of gene silencing following the introduction of double-stranded RNA (dsRNA) into cells. In mammalian cells, in order to avoid an interferon response, RNAi is conducted by using short interfering RNA, also known as siRNA, which may comprise two separate strands of RNA or a hairpin structures also known as shRNA, that may be processed by a cell into a short duplex that contains two different strands.
Lentiviruses have recently been viewed and tried as potential means of efficiently introducing shRNA into cells. When introduced into cells under conditions that permit the lentiviruses to act in their intended manners, these vectors have demonstrated the potential to be important tools for gene therapy.
As persons of ordinary skill in the art will recognize, lentiviruses, like other vectors, are often created and introduced into cells with internal promoter regions, which serve the function of providing control points for transcription. However, promoter activity can vary widely across cell lines and cell types. Inefficient promoter activity can result in poor expression, which can often be misinterpreted as unsuccessful delivery, unsuccessful genomic integration or in the case of shRNA-containing vectors, poor gene silencing efficiency.
Thus, there is a need to provide better options for permitting persons of ordinary skill in the art to select elements of their lentiviral vector constructs with greater likelihood that the constructs will effectively introduce the desired genetic element into any cell or organism and express the desired genetic elements in the cell or organism.